20121231

An article on an online science and science fiction discussion blog(*) discusses the past history and possibility of future colonization of Mars:

So, what happened on Mars? When volcanic activity halted on Mars...this once warm and inviting place, with enough atmospheric pressure and a high enough temperature to support liquid water, become a frozen rock with [a thin] atmosphere...

Discuss how the end of volcanic activity on Mars caused temperatures to drop and its atmosphere to become thinner. Explain using the properties of greenhouse gases and geological activity.

p:Correct. Discusses features of the "runaway refrigerator" model of
Mars' past: (a) Mars' small mass would make it unable to retain its atmosphere
due to its slower escape velocity, (such that its atmosphere thins), and thus
(b) unable to retain enough heat (such that its temperatures will drop). May
also have discussed how Mars' oceans removed greenhouse gases from the
atmosphere.

r:Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. One of two
points (a)-(b) correct, other is problematic/incomplete.

t:Contains right ideas, but discussion is unclear/incomplete or contains major errors. Both points (a)-(b) problematic/incomplete, or one point
correct while other is missing.

v:Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least understands factors
that contribute to atmosphere retention and greenhouse effect.

x:Implementation/application of ideas, but credit given for effort rather than merit. Discusses factors other than relevant to atmosphere
retention and greenhouse effect.

p:Correct. The online comment is correct, as Ceres needs to satisfy
the first two of the three IAU requirements (orbits the sun, has a rounded
shape, cleared/dominates its orbit) to be a dwarf planet, and would otherwise be
classified as an asteroid if it only satisfied the first requirement.

r:Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Discussion of
IAU requirements, or why online comment is correct is not clear.

t:Contains right ideas, but discussion is unclear/incomplete or contains major errors. Problematic discussion of IAU requirements and why
online comment is correct.

v:Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discussion only tangentially
related to the IAU requirements.

x:Implementation/application of ideas, but credit given for effort rather than merit. Discussion unrelated to the IAU requirements.

A Physics 205A student kicks a ball off the edge of a cliff with an initial velocity that is directed 45° below the horizontal, and the ball hits the ground below 3.0 s later. Discuss why the average speed of the ball will be greater than the magnitude of the average velocity as it falls to the ground. Explain your reasoning using the properties of distance traveled, displacement, and elapsed time.

Solution and grading rubric:

p:Correct. Understands distinction between average speed (distance
traveled divided by elapsed time) and magnitude of average velocity (magnitude
of displacement divided by elapsed time), and clearly indicates how the distance
traveled by the ball is greater than the magnitude of displacement during its
trajectory towards the ground.

r:As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Does not explicitly discuss how distance traveled is greater than the magnitude
of displacement for this trajectory (as most generally it is possible for the
distance traveled to be equal to the magnitude of the displacement).

t:Nearly correct, but argument has conceptual errors, or is incomplete. At least distinguishes between distance traveled and magnitude of displacement.

v:Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discussion based on some other
aspect of kinematics, vectors, and differential calculus.

x:Implementation/application of ideas, but credit given for effort rather than merit. Discussion based on concepts other than kinematics, vectors,
and differential calculus.

A string has its tension set by a hanging mass M, and resonates at its fundamental frequency at 150 Hz. This same string will resonate with two antinodes at 150 Hz when a different mass m is hanging from it. Discuss why M > m. Explain your reasoning using the properties of wave speeds, periodic waves, and standing waves.

Solution and grading rubric:

p:Correct. Understands how (a) the fundamental frequency is
proportional to wave velocity, and (b) the wave velocity depends on the square
root of the mass creating the tension, and (c) the string vibrating at its
second harmonic has a fundamental frequency half that of the other string, such
that the second harmonic vibrating string has a slower wave velocity, a lower
tension, and thus a smaller hanging mass.

r:As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes.

t:Nearly correct, but argument has conceptual errors, or is incomplete.

v:Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least understands how the
hanging mass affects tension, and thus wave velocity.

x:Implementation/application of ideas, but credit given for effort rather than merit.

A 0.50 m long steel bar has same cross-sectional area as a 1.00 m long steel bar, and are both initially at room temperature (25° C). The same amount of heat is evenly applied to each bar. Discuss why both bars would expand by 0.0001 m from their original lengths. (Ignore heat lost to the environment.) Explain your answer using the properties of heat, internal energy, temperature, and thermal expansion.

Solution and grading rubric:

p:Correct. Same heat is applied to each bar, but:

the shorter bar
is half the mass of the longer bar, such that the increase in temperature of the
shorter bar will be twice that of the longer bar.

the shorter bar has
half the length, but twice the temperature change compared to the longer bar,
and so the length expansion (which is proportional to both the original length
and temperature increase) will be the same compared to the longer bar.

r:As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. At least recognizes that (1) bars experience different temperature changes, and
(2) expansion of bars depends on both original length and temperature change.

t:Nearly correct, but argument has conceptual errors, or is incomplete.

v:Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. May instead argue that same
cross-sectional area is relevant factor, or same temperature change for both
bars, etc. At least discussion based on thermal expansion and/or heat capacity.

x:Implementation/application of ideas, but credit given for effort rather than merit. Discussion based on phenomena other than thermal expansion
or heat capacity.

A 0.50 m long steel bar has twice the cross-sectional area as a 1.00 m long steel bar. The bottom of each bar is immersed in 20° C water, while the top of each bar is heated to 80° C. (Ignore the very slight thermal expansion of these bars). Discuss why the 0.50 m bar will conduct more heat per time than the 1.00 m bar. Explain your answer using the properties of heat, temperature, and heat transfer.

Solution and grading rubric:

p:Correct. Heat is conducted from the top to the bottom of each bar,
at a rate (1) proportional to the cross-sectional area, and (2) inversely
proportional to the length, such that the wider, shorter bar will conduct heat
at a rate four times faster than the narrower, longer bar.

r:As (p), but argument indirectly, weakly, or only by definition supports the statement to be proven, or has minor inconsistencies or loopholes. Typically argues only (1) area, or only (2) length as a factor in why the wider,
shorter bar will conduct heat faster than the narrower, longer bar.

t:Nearly correct, but argument has conceptual errors, or is incomplete.

v:Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least recognizes different
factors (1)-(2) and attempts to discuss heat conduction along the length of the
bars.

x:Implementation/application of ideas, but credit given for effort rather than merit. Discussion based on phenomena other than heat conduction along
the length of the bars.

A 3.0 kg box on a horizontal table is attached by a string to a hanging 1.2 kg mass. The string and pulley are ideal, but the table is not frictionless. A Physics 205A student observes that the 1.2 kg hanging mass is just sufficient enough to overcome static friction between the 3.0 kg box and the table. The student resets this experiment, adding 0.1 kg to the box, and 0.1 kg to the hanging mass. Determine whether static friction between the box (now 3.1 kg) and the table would be overcome by the hanging mass (now 1.3 kg). Show your work and explain your reasoning using a free-body diagram, the properties of forces, and Newton's laws.

Solution and grading rubric:

p:
Correct. Draws free-body diagrams, and applies properties of forces
and Newton's laws to determine the static friction coefficient between the box
and table for the first case; then for the second case determines that static
friction would be overcome for the box either by discussing how (a) the hanging
mass will exert a tension force on the box greater than the maximum static
friction force on the box, or (b) the required static friction coefficient
between the box and table to remain stationary is greater than the static
friction coefficient in the first case, and since the static friction
coefficient remains constant, the static friction on the box will again be
overcome.

A 0.30 kg cart is held against a spring that is compressed by 0.040 m. After the 0.30 kg cart is released from the spring, it travels horizontally with a velocity of +0.45 m/s and collides and sticks together with a 1.50 kg cart that was initially at rest. Neglect drag and friction. Find (a) the spring constant of the spring, and (b) the final velocity of the two stuck-together carts. Show your work and explain your reasoning.

t:
Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. Appropriate conservation law applied for one of
(a) or (b) with correct or nearly correct result, other typically has misapplied
conservation law (using momentum conservation when only mechanical energy is
conserved, or kinetic energy conservation when only momentum is conserved).

v:
Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. Some attempt at applying some conservation law.

x:
Implementation of ideas, but credit given for effort rather than merit. No clear attempt at applying conservation laws.

p = 20/20:
Correct. Determines (a) rotational inertia of each wind turbine by
summing the individual rotational inertiae of each component blade, and (b)
equates rotational kinetic energies, such that the wind turbine with the smaller
rotational inertia must have the faster rotation rate. (May have neglected to
square rotational speed in expression for rotational kinetic energy in (b),
either due to confounding rotational kinetic energy with angular momentum, or
careless algebra.)

r = 16/20:
Nearly correct, but includes minor math errors. One of (a) or (b) is
correct, other part is substantive and nearly complete.

t = 12/20:
Nearly correct, but approach has conceptual errors, and/or major/compounded math errors. Substantive but problematic efforts in both (a)
and (b); or one of (a) or (b) is nearly correct, but other is missing or
insubstantive.

v = 8/20:
Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner.

x = 4/20:
Implementation of ideas, but credit given for effort rather than merit.

20121219

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions and comments were asked on the last reading assignment of the semester.

Selected/edited responses are given below.

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"If I have to repeat this course would you recommend taking the lab with it?" (Not unless you are required to satisfy a science laboratory breadth requirement, and/or are very interested in satisfying your curiosity of astronomy and research in science. Otherwise the laboratory is an adjunct course that is not absolutely mandatory for success in lecture.)

"If you could live on any planet besides Earth, which would you choose and why?" (That recently discovered habitable-zone planet around Tau Ceti, 12 light years away, sounds like a pretty interesting place to live.)

"Was Mrs. P-dog really a cheerleader?" (Yes. In my dreams.)

"Since it is the holiday season, maybe you should consider not making the final too challenging. Maybe?" ("...Tests are a gift. And great tests are a great gift. To fail the test is a misfortune. But to refuse the test is to refuse the gift, and something worse, more irrevocable, than misfortune." --Lois McMaster Bujold, Shards of Hono)

"Why did you decide to teach astronomy if you have never taken an astronomy course?" (Because even more awesome than being able to learn astronomy, is being able to teach astronomy.)

"At the beginning of this course I stated that I was going to change your perception of what an 'A' student is capable of... Did I succeed?" (Yes. But every one of my 'A' students has surprised me in their own way.)

20121216

Nucleosynthesis in the first few minutes after the start of the big bang produced the:
(A) lithium in hybrid car batteries.
(B) hydrogen in Jupiter's atmosphere.
(C) iron in your blood.
(D) calcium in your bones.
(E) (More than one of the above choices.)
(F) (None of the above choices.)

Correct answer: (A)

Hydrogen is merely the raw ingredient of the universe. Light nuclides such as deuterium, helium and lithium are produced by fusion of hydrogen in the cores of main sequence stars, but deuterium and lithium are typically broken apart by the high pressures and temperatures there, such that stars cannot have produced any of the deuterium and lithium present in the universe today. These light nuclides were also produced by similar conditions in the first few minutes after the start of the big bang, but as the universe expanded and cooled, deuterium and lithium that would have been broken apart were preserved and these "fossil" nuclides remain to this day. Iron and calcium are heavier elements that can only be produced in the last stages of a supergiant, and would be dispersed to the rest of the universe during a subsequent type II supernova.

20121215

__________ on Venus' surface may be evidence that its crust was replaced within the last half-billion years.
(A) Widespread faults and folded mountain ranges.
(B) Lack of sedimentary rocks.
(C) Long curving ridges that cut through craters.
(D) The small number of craters.

Correct answer: (D)

The density of impact craters on the surface of a terrestrial planet is correlated with the solidification age of the crust: fewer craters corresponds to more recent solidification of the crust. The lack of plate tectonics on Venus along with its small number of craters indicates that the crust may have been replaced by widespread volcanism relatively recently.

Lack of __________ on Venus' surface may be evidence it does not have plate tectonics.
(A) volcanic activity.
(B) sedimentary rocks.
(C) widespread faults and folded mountain ranges.
(D) oceans.

Correct answer: (C)

Plate tectonics ("continental drift") on Earth results in characteristic midocean rifts (where new crust is formed from the mantle) and subduction zones (where older crust is folded back down into the mantle), but also results in faults, where crustal plates move laterally past each other, and folded mountain ranges, where crustal plates are compressed and crumpled up. Lack of these features indicates that Venus does not have plate tectonics as does Earth.

Belts and zones on Saturn are less visible than on Jupiter because they:
(A) are periodically impacted by Saturn's ring particles.
(B) have light reflected from Saturn's rings.
(C) have a metal-poor composition.
(D) lie deeper down in Saturn's atmosphere.

Correct answer: (D)

The topmost cloud layers of Jupiter and Saturn's belts and zones are warmed by sunlight; these layers are warmer for Jupiter and cooler for Saturn, such that Saturn's clouds are less buoyant and lie lower, obscured by haze.

Uranus and Neptune are referred to as ice giants because they:
(A) are jovian planets located furthest from the sun.
(B) have prominent polar ice caps.
(C) are rich in liquid and solid forms of water.
(D) have icy rather than rocky moons.

Correct answer (highlight to unhide): (C)

While Uranus and Neptune are farthest from the sun, their atmospheres (still being primarily composed of hydrogen and helium) have a greater proportion of various forms of water than does Jupiter and Saturn.

Of the following choices, which solar system object(s) only satisfies qualification I, but does not satisfy qualifications II and III?
(A) Mars' moon, Phobos, a captured asteroid.
(B) Makemake, a dwarf planet.
(C) Earth's moon.
(D) Mercury.
(E) (More than one of the above choices.)
(F) (None of the above choices.)

Correct answer: (F)

Phobos and Earth's moon both do not directly orbit the sun (qualification I). Makemake and Mercury both directly orbit the sun (qualification I), but are both rounded in shape (qualification II), while Mercury also dominates its orbit around the sun (qualification III). Thus none of these choices satisfies Both Almatheta and Earth's moon do not meet qualification I, but does not satisfy qualifications II and III.

Cruithne, an irregularly shaped body sharing Earth's orbit around the sun, is sometimes referred to as "Earth's second moon[*]." According to the IAU qualifications, Cruithne is classified as:
(A) a moon.
(B) solar system debris.
(C) a dwarf planet.
(D) a planet.
(E) (None of the above choices.)

Cruithne orbits the sun directly, so it is not a moon. However, due to its irregular shape, it is classified as solar system debris. (If Cruithne were rounded in shape, it would be classified as a dwarf planet, as it does not dominate its orbit around the sun.)

The international prototype meter[*][**] was set by the distance between two markings on a platinum-iridium alloy bar (α = 8.7×10–6 K–1). What temperature increase would correspond to the distance between these markings expanding by 0.01 mm?
(A) 0.001° C.
(B) 0.01° C.
(C) 0.1°.
(D) 1° C.

A 0.085 kg Whiskey Disk™ made of soapstone[*][**] at –10° C is placed into 0.22 kg of whiskey[***] at a temperature of 25° C. Ignore the effects of evaporation and phase changes, and heat exchanged with the environment and container. Specific heat of soapstone is 98 J/(kg·°C). Specific heat of whiskey is 3,400 J/(kg·°C). After reaching thermal equilibrium, the __________ had the greatest change in temperature.
(A) 0.085 kg Whiskey Disk™.
(B) 0.22 kg of whiskey.
(C) (There is a tie.)
(D) (Not enough information is given.)

A steel bar has twice the cross-sectional area as another steel bar of the same length. The bottom of each bar is immersed in 0° C water, while the top of each bar is heated to 75° C. (Ignore the very slight thermal expansion of these bars). The wider bar has ________ the thermal resistance of the narrower bar.
(A) one-fourth.
(B) one-half.
(C) twice.
(D) four times.
(E) (There is a tie.)

Correct answer: (B)

The thermal resistance R is given by:

R = d/(Κ·A),

where d corresponds to the (identical) length of these bars, Κ is the (identical) thermal conductivity of these bars, and A is the cross-sectional area of the bars. With Awide = 2·Anarrow, then for these two bars:

Rwide = d/(Κ·Awide),

Rnarrow = d/(Κ·Anarrow),

The wider bar will have one-half the thermal resistance of the narrower bar:

The power generated by NASA's Voyager 1 spacecraft was 420 watts in 1977, but today only 285 watts are generated.[*] Assume that all of this power is radiated into space (taken to be absolute zero). Neglect changes in the spacecraft's dimensions due to temperature changes, and assume that it is an ideal blackbody. If the surface temperature of Voyager 1 now is 194 K[**], the temperature of Voyager 1 in 1977 was:
(A) 210 K.
(B) 290 K.
(C) 470 K.
(D) 780 K.

20121211

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

Describe something you found interesting from the assigned textbook reading or presentation preview, and explain why this was personally interesting for you.

"The Julia Child video--comical yet informational. Anything that can make a student laugh automatically captures attention and makes the topic much more interesting."

"All life on Earth is made possible by carbon atoms. Just crazy it can be pinpointed to a single element."

"How long it took to evolve from simple compounds into complex organisms we have today. In my anthropology class we thoroughly discuss how humans have evolved from primates, but it took billions of years just to get to that point!"

"How DNA correlates to heredity and genetics. We all have genes from our mother and father and it's amazing if there are more than one offspring that each one can pick up different genes. For example a family of four the daughter could look just like the father's side of the family and the son can look like the mother's side. At the same time they both still look related."

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"Doesn't it frustrate you that we will never know everything about our universe?" (That aspect of astronomy means that there will always be new and exciting things to be discovered.)

"Do you round up if our points are close to a grade cut-off?" (You do that. You round your own points up by doing the extra-credit assignments. Otherwise, if you haven't done any of them, then that won't happen.)

"Did you enjoy this semester P-dog?" (Yes. But I say that every semester.)

"Do you believe in life on other planets?" (Yes, I do. I would be willing to bet a dollar that there is (or was) life on other planets.)

"My co-worker told me that NASA found out that on December 21, 2012 the world will go dark for three days. Is that true?" (Tell your co-worker: yes. Totally going to happen. NASA would never lie. Your astronomy teacher would never lie. More seriously, check out how the Mayan calendar will roll over from the 12th to the 13th 'long-count' on December 21, 2012.)

Students at both Cuesta College (San Luis Obispo, CA) and the University of California at Davis were administered the 30-question Force Concept Inventory (Doug Hestenes, et al.) during the last week of instruction.

This Hake gain is in line with the previous semesters' results for algebra-based introductory physics at Cuesta College (0.25-0.33), and greater than previous gains for algebra-based introductory physics at UC-Davis (0.16), and for calculus-based introductory physics at Cuesta College (0.14-0.16), as discussed in previous postings on this blog.

Notable about this Physics 205A class at Cuesta College during this fall 2012 semester is the requirement that students read and answer questions on the textbook and lecture slides before coming to lecture (in a "flipped classroom"), and the continuing use (since fall semester 2011) of flashcards rather than electronic response system "clickers" (Classroom Performance System, einstruction.com), to engage in "think-pair-share" (peer-instruction).

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

"Interesting but scary finding out that humans are fairly recent living creatures. I wonder what will be the next living things or people. Amazing how things change within a blink of an eye (relatively speaking)."

Describe something you found confusing from the assigned textbook reading or presentation preview, and explain why this was personally confusing for you.

"Life, man. Where we came from, and why?"

"The Drake equation. It looks like a long list of random letters and numbers put together. Who would come up with an equation that they can't find all the factors for?"

"Why there isn't evidence of the first forms of 'life.'"

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"How many more homework assignments do we have? If we have the maximum amount for homework assignments is there a point in doing the assignments, besides for our own good?" (One more, after this. And yes, you can't get more points after maxing out your homework score.)

"Can you give us all 'A's' on the Final Exam as a Christmas present?" (I can do better than that. I can give you all the gift of having the opportunity of earning an 'A' for Christmas. Unless you've been naughty. Ho ho ho.)

"What are your views on the 12/21/12 'apocalypse?'" (That is the purported end of the 12th Mayan 'long count' cycle. They have a base-20 counting system, so presumably there would be eight more long counts Check out how the Mayan calendar will roll over from the 12th to the 13th 'long-count' on December 21, 2012.)

"Do you believe there are other intelligent life forms besides us?" (Yes, I do. I would bet one dollar that there is an advanced technological civilization somewhere out there.)

20121210

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

Students are assigned to read online articles on current astronomy events, and take a short current events quiz during the first 10 minutes of lab. (This motivates students to show up promptly to lab, as the time cut-off for the quiz is strictly enforced!)

20121209

Students have a weekly online reading assignment (hosted by SurveyMonkey.com), where they answer questions based on reading their textbook, material covered in previous lectures, opinion questions, and/or asking (anonymous) questions or making (anonymous) comments. Full credit is given for completing the online reading assignment before next week's lecture, regardless if whether their answers are correct/incorrect. Selected results/questions/comments are addressed by the instructor at the start of the following lecture.

The following questions were asked on reading textbook chapters and previewing presentations on enrolling in the second semester of this general physics (Physics 205AB, algebra-based college physics) sequence.

Selected/edited responses are given below.

Next semester I am __________ take Physics 205B.

already enrolled in :

********************* [21]

planning to enroll in :

****** [6]

not planning to :

*********** [11]

(not yet sure/undecided) :

******** [8]

If you are not taking Physics 205B next semester, are you planning on enrolling in a later semester?

Yes. :

*********** [11]

Maybe. :

*********** [11]

No. :

*************** [15]

Ask the instructor an anonymous question, or make a comment. Selected questions/comments may be discussed in class.

"I really want a 'B' in your class. really really badly." (Good. You won't get it unless you first want it.)

"I really enjoyed this class P-Dog. You definitely made this easier to understand than my high school teacher did." (I pity your high school physics teacher.)

"What kind of concepts do we learn in Physics 205B? Is 205B harder than 205A? Will you teach Physics 205B?" (Lenses, interference, electromagnetism, circuits, and some modern physics. Like the second-half of Physics 205A, we go through an average of one chapter a week. Yes, I will be there for you. Good times ahead.)

"How well do you think we did as a class this semester?" (We'll see how well you do on the conceptual Physics Survey B post-test, compared to UC-Davis students.)

"No question, but a comment. I absolutely love your way of grading. The way the scale is written out is my favorite out of any class I have had. I know exactly how many points I need to make it to the next grade at all times throughout the class. It may have been daunting to start with an 'F' and earn your way up to a better grade, but I think it just makes students try harder. Students don't have to worry about a bad test or quiz lowering your grade. Thank you."

"I thought I didn't have to take physics for my major, but I changed schools and now I need both semesters! I'm so glad I stuck with it. Thanks for being an awesome teacher!"

t = 12/20:Contains right ideas, but discussion is unclear/incomplete or contains major errors.

v = 8/20:Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. At least attempts to use
Wien's law, H-R diagram and/or the Stefan-Boltzman law.

x = 4/20:Implementation/application of ideas, but credit given for effort rather than merit. Discussion not based on Wien's law, H-R diagram and/or the
Stefan-Boltzman law.

An astronomy question on an online discussion board[*] was asked and answered:

dk: How can we tell that a star cluster is young (only 10 million years old or so)? Small, cool stars, [or] large, hot stars [on the main sequence]? pl: Large, hot stars [on the main sequence] means the cluster is young.

p:Correct. Understands that massive (large, hot) stars evolve faster
than low-mass (small, cool) stars, such a younger star cluster will have massive
stars that are on the main-sequence, while an older star cluster will have
low-mass stars on the main-sequence.

r:Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors.

t:Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least understands correlation between mass and main
sequence lifetimes.

v:Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner.

x:Implementation/application of ideas, but credit given for effort rather than merit. Discussion other than that of the properties and evolution
of stars.

[20 points.] An astronomy question on an online discussion board(*) was asked and answered:

P-dog: Can a star with apparent magnitudes of +1, and a star with apparent magnitude –1 have the same absolute magnitude? NoPlate: Yes, [if] the star with –1 [apparent] magnitude [is located] much closer...

Discuss why this answer is correct, and how you know this. Explain using the properties of apparent magnitude, absolute visual magnitude, and distance.

p = 20/20:Correct. Understands difference between apparent magnitude (m)
values and absolute magnitude (MV) values, and that the two stars can have the
same absolute magnitude (same brightness if both located 10 parsecs away) if the
star that is actually closer seems bright (m = +1) and the star that is actually
farther away seems dimmer (m = -1).

t = 12/20:Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least understands the difference between apparent (m) and absolute (MV) magnitudes, and that smaller
positive (or more negative) magnitudes are brighter.

v = 8/20:Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Garbled definitions/relations
between d, m, and MV.

x = 4/20:Implementation/application of ideas, but credit given for effort rather than merit. Discussion not based on apparent magnitudes, absolute
magnitudes, and distances.

p = 20/20:Correct. Understands that (a) stars in the same cluster are all born
at the same time, (b) massive stars evolve faster than medium-mass stars, and
(c) white dwarfs are the remnant of medium-mass stars (after going through its
giant and planetary nebula phases), such that it is not possible for a massive
star on the main-sequence to be the same age as a medium-mass star that has
already ended its main-sequence lifetime to become a white dwarf.

r = 16/20:Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. May confuse
white dwarfs (medium-mass stars that have long ago ended their main-sequence
lifetime) with red dwarfs (low-mass stars on the main-sequence).

t = 12/20:Contains right ideas, but discussion is unclear/incomplete or contains major errors. At least understands correlation between mass and main
sequence lifetimes.

v = 8/20:Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner.

x = 4/20:Implementation/application of ideas, but credit given for effort rather than merit. Discussion other than that of the properties and evolution
of stars.

[20 points.] An astronomy question on an online discussion board(*) was asked and answered:

strange questioner: Big bang: explosion or expansion? Most...sources say big bang as explosion, some others say it is wrong to say explosion and it's only expansion. green meklar: It is more like an expansion [than an explosion].

Discuss why this answer is correct, and how you know this. Explain using observations and evidence related to the Hubble law.

p = 20/20:Correct. Discusses (a) Hubble's law (recession velocity of galaxies
is proportional to distance), (b) evidence for Hubble's law (greater redshift of
absorption lines for distant galaxies compared to nearby galaxies), and (c)
relates this to the expansion of space, as opposed to an explosion (where the
velocity of particles is inversely proportional to the distance from the center
of the explosion, and also has a unique center).

r = 16/20:Nearly correct (explanation weak, unclear or only nearly complete); includes extraneous/tangential information; or has minor errors. Discusses two
of the three (a)-(c) points in (p).

t = 12/20:Contains right ideas, but discussion is unclear/incomplete or contains major errors. Discussion of only one of the three points (a)-(c) in
(p) is complete.

v = 8/20:Limited relevant discussion of supporting evidence of at least some merit, but in an inconsistent or unclear manner. Discussion based on evidence
of the earlier stages in the history of the universe, with little or no
substantive discussion of Hubble's law.

x = 4/20:Implementation/application of ideas, but credit given for effort rather than merit.